Manufacture of textryls



March 4, 1969 n c. WILSLIAMS ETAL 3,431,334

MANUFACTURE OF TEXTRYLS Filed Nov. 14, 1966 United States Patent 5 Claims ABSTRACT OF THE DISCLOSURE Process for the manufacture of a nonwoven synthetic fiber sheet comprising the simultaneous heating and compressing of an essentially dry textryl sheet comprising synthetic fibers and fibrids prepared on a Fourdrinier paper machine. The dry textryl sheet is simultaneously heated to a temperature sufiicient to bond the synthetic fibers with the fibrids and compressed against a smooth rigid surface at a pressure of at least 5 p.s.i.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of copending application Ser. No. 323,015, filed Nov. 12, 1963, now abandoned.

BACKGROUND OF THE INVENTION Nonwoven fabrics comprising fibrids and synthetic fibers as formed on a Fourdrinier paper machine are commonly referred to as textryls. A conventional method today for bonding continuous textryl fabrics after their manufacture is by calendering which comprises assing the continuous textryl between two rolls, one roll being a hard surface roll generally heated in the neighborhood of about 400 F. and the other roll being a soft surface member. While that method is suitable for the production of textryls of good quality, it has certain disadvantages. For one, it is a slow speed operation which generally requires several passes of the textryl sheet through the calendering unit. By slow is meant speeds anywhere from feet per minute upwards to as much as 200 feet per minute depending upon the type of operation, however in any case never equalling the full capabilities of a conventional Fourdrinier paper machine on which the textryl is usually formed. Or in other words, textryls have never been produced at rates on the order of a thousand or more feet per minute.

Production rates of textryls as produced above have been improved to some extent by preheating the textryl prior to entering the calender nip. In this manner, production rates as high as 450 feet per minute may be realized. However, this technique has its shortcomings in that the textryl web becomes extremely weak when heated prior to entering the calender nip and consequently may shrink up to as much as 10 percent. Moreover, it has been found that heating of the textryl when it is not under pressure greatly reduces the total obtainable bonding strength. Thus it can be seen that a method of bonding a continuous textryl sheet without incurring any shrinkage or sacrifice of bonding strength at production rates greater than 450 feet per minute, viz, on the order of 1000 feet per 3,431,334 Patented Mar. 4, 1969 minute or more, would be a welcome contribution to the art.

An object of this invention is to provide a process whereby nonwoven synthetic fiber sheets are bonded without incurring any shrinkage or sacrifice of bonding strength. A more specific object of this invention is to provide a process for the production of such textryls at production rates heretofore unobtainable in the art, viz, on the magnitude of 1000 feet per minute or greater. These and further objects will come to light as the discussion proceeds.

The drawing depicts an apparatus arrangement wherein the process of this invention can be practiced.

The above objects are achieved pursuant to the practice of this invention which provides a continuous process for bonding an essentially dry nonwoven synthetic fiber sheet composed essentially of synthetic fibers and fibrids, said process comprising passing said essentially dry sheet over a rigid surface; heating said sheet to a temperature at least suificient to bond the fibrids in said sheet; while uniformly compressing said sheet against a substantial portion of said rigid surface while in contact therewith, said pressure being at least about 5 psi. Generally, it is preferred to compress the sheet to a pressure within the range of from about 5 to about 500 p.s.i., especially from about 10 to about psi.

As can be seen in the drawing described in detail hereinafter, it is preferred to employ a heated drum upon which surface the teXtryl sheet is bonded under heat and pressure. A drum having a diameter of from about 2 to about 10 feet, especially around 4 to 6 feet, is preferred. The sheet is wrapped over the surface of the drum through an arc of from about to about 270, especially from about to about 240 when employing the preferred drum diameter.

As can be seen easily from this, a sheet in contact with a drum having a diameter of 2 feet for an arc of 60 will have a contact area of 41r square inches per inch of width of the sheet and 901r square inches per inch of width of the sheet for a 10 foot diameter drum using a contact are of 270. When using a drum of the preferred diameter range, the sheet contact area is from about 81r to about 541r square inches per inch of width of the sheet; and when the preferred are of contact and drum diameters are used, the sheet contact area is from about 1971 to about 4871' square inches per inch of width of the sheet. In all conversions above, 1r is the transcendental number having a value to eight decimal places of 3.14159265.

Translating this into terms of process: times, for most operations a time within the range of from about 0.1 to about 3 seconds, especially from about. 0.2 to about 1 second is suitable for bonding a textryl at a production rate of 500 feet per minute or greater.

In view of the above, a more preferred embodiment of the present invention is a continuous process for bonding an essentially dry nonwoven synthetic fiber sheet composed essentially of synthetic fibers and fibrids, said process comprising passing said sheet around and in direct contact with a drum surface, the extent of wrap of said sheet over said drum being within about 60 to about 270; heating said sheet to a temperature at least sulficient to bond the fibrids in said sheet; while uniformly compressing a substantial portion of said sheet against said drum surface by pressure belt means exerting a pres- 3 sure upon said textryl within the range of from about 5 p.s.i. to about 500 p.s.i.

In the bonding of textryls by the process of this invention it is preferred to employ a temperature within the range of from about 250 F. to about 650 F., especially between about 350 F. to about 550 F. Operating at these temperatures employing a textryl sheet having a weight of from about 0.5 to about 5.0 ounces per square yard, preferably however from about 1.0 to about 2.5 ounces per square yard, provides for the production of textryls having optimum properties at production rates on the order of those realized in the manufacture of conventional paper.

Textryls produced by way of the instant process are those derived from synthetic fibers, such as polyesters (e.g., polyethylene terephthalate), polyamides (e.g., polycaprolactam), and acrylic polymers (e.g., polyacrylonitrile) and fibrids, as derived from a similar synthetic fiber base as that of the particular synthetic fiber employed. The exact chemical composition of fibrids are not known to us, however they are described in the art as filmy or fibrous binder particles prepared from thermoplastic polymers similar in chemical composition to specific synthetic man-made fibers with which they are combined in the production of textryls. Exemplary of fibrids suitable for use in the instant process are those defined in US. Patent 2,988,782 and specific examples are those having Du Ponts product designations: 101 fibrids, designed to bond polyamide fibers; 201 fibrids, designed to bond polyester fibers; and 302 fibrids, designed to bond acrylic fibers.

Referring to the drawing which illustrates a preferred apparatus arrangement wherein the present process can be practiced, a textryl is fed to the bonding means comprising heated drum means 11 and pressure belt assemblies A, B, and C. The pressure belt assemblies further comprise, for example in assembly A, belt means 12 which is a continuous member conveyed over roller means 13, 14, and 15. Rollers 13 and 14 are spaced in closed proximity to drum 11 such that upon positioning roller 15 by tensioning means 16 acting thereon, belt 12 is caused to urged the desired amount of pressure against the textryl sheet 10 confined against the surface of drum 11. The drum 11 is preferably heated by steam, in which case drum 11 further comprises steam injection and discharge means. Generally, textryl 10 has a tendency to stick to the surface of drum 11 and metal belts 12, 17, and 22 and therefore it is preferred to coat such members with a nonadherent material, for example polytetrafluoroethylene or the like. This can be accomplished by either coating the members with a permanent sheet of such material of employing a lubricant comprisinmg such material.

In the embodiment illustrated, the amount of contact between textryl 10 and drum 11 is easily governed from about 60 up to about 270 by operation of the different pressure belt assemblies A, B, and C. For example, operation of any one given unit alone will provide for 90 of contact. Use of two pressure belt units will provide for 180 contact, e.g., operation of the units B and C. The pressure belt assembly A is equipped with a movable roller 13 such that incremental degrees of contact less than 90 can be achieved easily. Roller 13 is movable at a fixed radius around the longitudinal axis of the drum 11 such that as it is moved toward roller 14, the arc of contact between pressure belt 12 and textryl 10 is reduced. In this manner, incremental degrees of contact are easily achieved during operation without any interruption. Textryl 10, after being bonded, is taken off drum 11 over roller means 27. If desired, a cooled non-adherent smooth surface doctor blade 28 can be provided to effect rapid and clean separation of textryl 10 from drum 11.

It is understood of course that in the apparatus arrangement depicted in the drawing, a single pressure belt assembly could be employed in lieu of the three separate units as illustrated. In which instance, pressure belt 12 would be wrapped around the drum 11 to the extent required for a given set of conditions to cure or bond a particular textryl sheet.

By way of example, a 3 ft. diameter drum having a tetrafiuoroethylene polymer coating is employed to bind a textryl sheet comprising polyamide fibers and fibrids and having a weight of about 1.25 ounces per square yard. The sheet is passed over the drum surface through an arc of about 270 and at a speed of about 1200 feet per minute. A metal belt which also has a tetrafiuoroethylene polymer coating is caused to urge the sheet against the drum surface heated to a temperature of about 380 F. so as to impose a continuous uniform pressure of about 45 p.s.i. against the traveling sheet which pressure is maintained for about 0.4 second. After bonding, the textryl sheet is found to be a dense fabric having a smooth surface and high tensile strength.

In another run, a 4 ft. diameter drum having a nonadherent surface and heated to a temperature of about 330 F. is employed to bind a one ounce per square yard textryl sheet comprising fibers and fibrids derived from polyester polymers. The sheet is caused to contact the nonadherent drum surface over an arc of about 225 while traveling at a rate of about 1600 feet per minute. The pressure belt means having a non-adherent surface is caused to press the sheet against the drum surface so as to exert a pressure upon the sheet of 60 p.s.i. Thus, a given segment of the sheet material is maintained under these conditions for a period of time of about 0.3 second. The polyester sheet is found to be dense and of high tensile strength.

Employing a similar weight sheet as above except at a production rate of 900 feet per minute and a pressure of around 30 p.s.i. produces similar results.

When a 5 ft. diameter drum is employed to bond a 1.75 ounces per square yard textryl sheet composed of fibers and fibrids derived from acrylic polymers, at a production rate of 1000 feet per minute, a drum temperature of about 280 F., and a belt pressure of 20 p.s.i., a smooth surface sheet having high tensile strength is produced. The sheet is subjected to the above conditions for about 0.6 second.

In this run, a 7 ft. diameter drum heated to about 240 F. and having a non-adherent surface is employed to bind a fabric composed of natural cellulose and polyester fibrids and fibers having a weight of about 2.25 ounces per square yard. The fabric is caused to contact the drum surface over an arc of about 180 and is subjected to a pressure of aboot 12 p.s.i. At a production rate of 800 feet per minhte the web is subjected to these conditions for about 0.9 second. The resultant fabric is found to have a fairly smooth surface and good tensile strength.

Thus it can be seen from the above that the process of this invention provides a method for producing textryls of high strength and at high production rates, viz, on the magnitude of that realized in conventional papermaking processes.

What is claimed is:

1. A continuous process for preparing a substantially smooth surface textryl sheet having a weight of from about 0.5 to about 5.0 ounces per square yard from an essentially dry nonwoven synthetic fiber sheet composed essentially of synthetic fibers and fibrids which process comprises, in combination, the simultaneous steps of,

(a) passing said essentially dry nonwoven synthetic fiber sheet around and in direct contact with a rotating substantially smooth cylindrical drum surface for a circumferential contact area comprising from about 41r to about 9O1r square inches per inch of width of said sheet;

(b) heating said essentially dry nonwoven synthetic fiber sheet while in contact with said drum surface to a temperature of from about 250 F. to about 5 650 F. to bond said synthetic fibers by means of said fibrids While retaining the fiber integrity;

(c) uniformly compressing substantially all said sheet while in contact With said are of said drum surface for a period of time of from about 0.1 to about 3.0 seconds by a continuous surface pressure belt means exerting a pressure upon said sheet of from about 5 p.s.i. to about 500 p.s.i.; and

(d) recovering the resulting smooth surface textryl sheet having fiber integrity and high tensile strength.

2. The process of claim 1 further characterized by said pressure being from about 10 p.s.i. to about 50 psi.

3. The process of claim 1 further characterized by said contact area being from about 191,- to about 4811- square inches per inch of Width of said sheet.

4. The process of claim 1 further characterized by said period of time being from about 0.2 second to about 1.0 second.

5. The process of claim 1 further characterized by said temperature being from about 350 F. to about 550 F.

References Cited UNITED STATES PATENTS 6/1961 Parrish et a1. 264-141 6/1962 Smith et al 26476 US. Cl. X.R. 

